Using the Polymarket Data API: Real-Time Prediction Market Data for Developers | March Madness Predictions

In this guide

Available Data Endpoints
Python Quickstart
Use Cases
FAQ

Real-time data from prediction markets has grown increasingly important across research, journalism, and algorithmic trading. PolyGram grants developers access to comprehensive APIs built on top of the world's most active prediction market infrastructure.

Available Data Endpoints

Gamma API (Market Data)

GET https://gamma-api.polymarket.com/events
  ?limit=100&active=true&order=volume24hr
  Returns: event metadata, current prices, volume, tags

GET https://gamma-api.polymarket.com/events/{slug}
  Returns: full event with all markets, prices, descriptions

GET https://gamma-api.polymarket.com/markets/{conditionId}
  Returns: single market details, current order book price

CLOB API (Order Book)

GET https://clob.polymarket.com/book
  ?token_id={tokenId}
  Returns: full order book depth (bids/asks)

GET https://clob.polymarket.com/prices/history
  ?market={conditionId}&resolution=1h&startTs=1700000000
  Returns: hourly price history

WebSocket: wss://ws-subscriptions-clob.polymarket.com
  Subscribe to real-time price updates

Python Quickstart

import requests

# Get top prediction markets by volume
r = requests.get(
    "https://gamma-api.polymarket.com/events",
    params={"limit": 10, "active": "true", "order": "volume24hr"}
)
for event in r.json():
    market = event["markets"][0] if event.get("markets") else {}
    prices = market.get("outcomePrices", "[0.5,0.5]")
    import json; p = json.loads(prices)
    print(f"{event['title'][:50]}: YES={float(p[0]):.2%}")

Use Cases

Research dashboards: Monitor probability shifts across prediction markets throughout an event's lifecycle
News tools: Identify markets gaining momentum following major announcements
Aggregators: Synthesise odds from Polymarket, Kalshi, and Metaculus in a single interface
Alert systems: Trigger notifications whenever a market swings past predetermined levels
Academic research: Leverage historical resolution data to evaluate forecast performance metrics

FAQ

Is the Polymarket API free to use?: Yes — market data (Gamma API) is available at no cost subject to rate limits (~100 req/min without authentication). CLOB order submission requires an active wallet, though data retrieval remains complimentary.
Is there a Python library for Polymarket?: Multiple community-driven Python libraries are available via GitHub. Look for "polymarket-py" to locate actively maintained versions.